1. Field of the Invention
The present invention relates to an image pickup apparatus such as a digital still camera and a digital video camera, and particularly to an image pickup apparatus having an auto zoom function capable of automatically keeping a constant size of an object in a captured image.
2. Description of the Related Art
Some image pickup apparatuses detects in an image (captured image) produced by using an image pickup element a specific object such as a person's face, and performs autofocus on the detected specific object. Moreover, Japanese Patent Laid-Open No. 09-149311 discloses an image pickup apparatus provided with an auto zoom function capable of performing zoom control so as to keep the size of a detected specific object constant in a captured image even though the distance to the specific object changes. Such an auto zoom function (hereinafter also referred to as “auto zoom”) stores the size of the specific object in the captured image at its start time as a reference size, and automatically performs the zoom control in a telephoto direction or in a wide-angle direction so as to make the size of the specific object detected thereafter equal to the reference size.
Furthermore, zoom lens units as image taking optical systems being installed in or detachably attached to image pickup apparatuses include a so-called inner focus type lens unit in which a focus lens is disposed further on an image side than a magnification-varying lens (zoom lens). Japanese Patent Laid-Open No. 2005-121752 discloses an inner focus type lens unit that stores plural electronic cams shown in FIG. 9 as data, and selects one of the electronic cams corresponding to a detected object distance. Then, this inner focus type lens unit moves the zoom lens and the focus lens so as to trace the selected electronic cam, thereby performing zooming (variation of magnification while maintaining an in-focus state).
As shown in FIG. 9, from a telephoto side to a wide-angle side, the plural electronic cams become converged, in other words, gaps among the plural electronic cams become reduced. Therefore, when the zoom lens is moved from the telephoto side to the wide-angle side, the in-focus state can be easily maintained by the above electronic cam tracing method. However, from the wide-angle side to the telephoto side, the plural electronic cams become diverged. Thus, it may be impossible to determine one electronic cam to be traced, which may make it difficult to maintain the in-focus state or may require a long time to obtain the in-focus state again after falling into an out-of-focus state.
In addition, starting the zoom control by the auto zoom in the out-of-focus state makes it difficult to obtain the in-focus state in the auto zoom.